Digit transmission over wireless communication link

ABSTRACT

A communication system having a wireless trunk for connecting multiple phone lines over wireless communication links to a cellular network comprises a central telephone switch, such as a private branch exchange or key system, connected through one or more trunk lines to a wireless access communication unit. The wireless access communication unit preferably comprises a separate subscriber interface for each trunk line from the central telephone switch. The wireless access communication unit collects data from each of the subscriber interfaces, formats the data into a format compatible with an over-the-air protocol, and transmits the information over one or mole wireless channels to a cellular base station. The wireless access communication unit thereby connects calls received from the central telephone switch&#39;s trunk lines over a wireless trunk to a network. A controller within the wireless access communication unit interfaces the subscriber interfaces with a radio transceiver, and assists in the conversion of data from a format suitable for wireless transmission. To initiate a call, the wireless access communication unit transmits digits to the base station, which performs digit analysis and sets up the call. During an active call, the wireless access communication unit transmits digits (e.g., DTMF tones) to the network using DTAP start and stop messages. The DTMF tones can be regenerated at the network.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.08/987,893, filed Dec. 10, 1997, and assigned to the assignee of thepresent application now U.S. Pat. No. 6,526,026.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The field of the present invention relates to a method and system forproviding communication services, including a method and system fortransmitting digits (such as DTMF tones) over a communication path.

2) Background

Localized telephone switching systems such as private branch exchanges(PBXs) and key type systems have for many years been available tobusiness offices and other establishments as an alternative or adjunctto public telephone service. A PBX or key system allows users connectedto the system to place intra-system telephone calls without accessingthe public telephone service. Such a system can provide significanteconomic benefits, particularly if intra-system telephone traffic isheavy.

On the other hand, when callers using a PBX or key system need to placea call to a party not connected to the system, such outside calls musttypically be routed through the PBX or key system controller overlandlines to the public telephone company. To accommodate such dualfunctionality (i.e., intra-system call support and outside callsupport), special-purpose telephones have been developed for connectionto a PBX or key system to allow manual routing of telephone calls. Forexample, deskset telephones can be provided with buttons correspondingto different telephone lines. By depressing the appropriate button, theuser selects between certain designated lines for calls within thesystem, or different designated lines for calls over the publictelephone network.

In other PBX and key systems call routing over the selected lines may beautomatic. For example, the user may select an intra-system call or acall over the public telephone network according to the first digitdialed, and the PBX or key system then analyzes the first digit androutes the call to the proper destination using the appropriate vehicle.

While PBX and key systems are useful for providing economical coveragewithin a private local telephone system, for long distance the PBX usersor key system users may still be required to rely on a local exchangecarrier (LEC) whose landlines are connected to the PBX. The localexchange carrier then routes the call to along distance carrier. Becausethe user must pay both the local exchange carrier and long distancecarrier for each long distance telephone call, long distance telephoneservice can be quite costly, particularly if the volume of long distancecalls is large.

Besides high costs for long distance service, another potentialdisadvantage of existing PBX or key telephone systems is that deploymentcan be difficult or expensive in remote areas. For example, if longdistance service or other public network services are required, thendeployment of a PBX or key system is generally limited to wherelandlines have been laid, so that the PBX or key system can have aconnection to a local exchange carrier which connects to the longdistance provider. If no landlines are present in the desired deploymentlocation, then it can be expensive to connect landlines to provide longdistance access for the PBX or key system. Also, conventional PBX or keysystems are generally not very mobile where they require an interfacewith landlines for long distance access or other types of public networkservices.

There is a need for a communication system having the ability of a PBXor key telephone system to manage local area calls, yet also which canprovide access to lower cost, reliable long distance or other networkservices. There is also a need for a versatile mechanism for allowingPBX or key type systems to achieve relatively inexpensive access tonetwork resources and long distance coverage. There is also a need for acommunication system that employs a robust, flexible protocol forproviding long distance coverage or other network services to localusers of a PBX, key system or other type of local area network.

SUMMARY OF THE INVENTION

The invention provides in one aspect a communication system having awireless trunk for connecting multiple phone lines over wirelesscommunication links to a cellular network. In one embodiment of theinvention, a central telephone switch or customer premises equipment(CPE), such as a private branch exchange or key system, is connectedthrough one or more trunks to a wireless access communication unit. Thewireless access communication unit provides the CPE with one or morewireless communication channels to a cellular network. Calls may beselectively routed by the CPE over landlines to a network or, instead,to the wireless access communication unit, thereby bypassing landlines.Multiple wireless access communication units in a geographical regioncan communicate with a single base station of the cellular network, solong as the base station capacity and current traffic load permit.

In another aspect of the invention, a wireless access communication unitis provided which has multiple trunk interfaces for connection to a CPE,and a radio transceiver for establishing one or more wirelesscommunication links to a cellular network. Each trunk interface isconnected to a line card comprising a vocoder and a subscriberinterface. A controller interfaces the line cards with the radiotransceiver, and assists in the conversion of data from a formatsuitable for wireless transmission to a format suitable for transmissionover the CPE trunk, and vice versa. Data communicated between thewireless access communication unit and the network may be encrypted atthe wireless access communication unit and decrypted at the mobileswitching center or else at a separate transcoding unit interposedbetween the mobile switching center and the base station subsystem.

In another aspect of the invention, dialed digits (such as DTMF tones)are transmitted over a communication path that includes at least onewireless link. At call setup, dialed digits are transmitted from thewireless access communication unit to the base station as signalingmessages. During an active call, dialed digits are transmitted from thewireless access communication unit to the network using GSM DTAPmessages to indicate the start and stop of each digit. The DTAP messagesare relayed transparently through the base station subsystem.

In a preferred embodiment of the invention, the wireless accesscommunication unit operates according to a protocol utilizing aspects offrequency division multiple access (FDMA), time division multiple access(TDMA) and/or code division multiple access (CDMA), wherebycommunication channels are assigned to the wireless communication uniton a demand basis. In a preferred embodiment, communication between thewireless access communication unit and a base station of the cellularnetwork is carried out over a plurality of wireless duplex communicationchannels, one channel for each CPE trunk, with base transmissions intime slots on one frequency band and user transmissions (including thosefrom the wireless access communication unit) in time slots on adifferent frequency band. In such an embodiment, the user time slots maybe offset in time from the base time slots, and radio transmissions maybe carried out using spread spectrum techniques.

In another aspect of the invention, the wireless access communicationunit registers each CPE trunk to which it is connected such that eachCPE trunk appears as a subscriber to the network. Each CPE trunk maytherefore be addressed by a unique subscriber identifier. The wirelessaccess communication unit preferably utilizes aspects of GSM signalingto communicate information to the network, such that communication witha GSM-based network is carried out transparently by the wireless accesscommunication unit.

In yet another aspect of the invention, the wireless accesscommunication unit periodically re-registers each of its CPE trunks. Thebase station receives and monitors the re-registration signals from thewireless access communication unit and, if the re-registration signalsare absent for a predefined period of time, issues an alarm message tothe network. The wireless access communication unit may be provided witha unique equipment identifier so that the base station can correlate thedifferent wireless links to a single wireless access communication unit.

Further embodiments, modifications, variations and enhancements of theinvention are also disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an overall system architecture in accordance witha preferred embodiment of the present invention.

FIG. 2 is a block diagram of a basic architecture for a wireless accesscommunication unit in accordance with various aspects of the presentinvention.

FIG. 3 is a diagram of a software architecture for the wireless accesscommunication unit of FIG. 2.

FIG. 4 is a block diagram of a basic architecture for a base station.

FIG. 5 is a diagram of a software structure for the base station of FIG.4.

FIG. 6 is a block diagram illustrating addressing of multiple trunksconnected to a wireless access communication unit according to apreferred embodiment of the present invention.

FIG. 7 is a diagram illustrating an interface signaling structurebetween a base station and a base station controller.

FIG. 8 is an abstract diagram of a system protocol architecture.

FIG. 9 is a diagram illustrating a division of bearer path functionsamong a wireless access communication unit (CPRU), base station and basestation controller components of a preferred communication system.

FIG. 10 is a diagram showing interfaces between the different componentsof a preferred system.

FIG. 11 is a diagram of multiple wireless access communication units indifferent location areas connected to a single base station controller.

FIG. 12 is a call flow diagram for a network-level registrationprocedure.

FIG. 13 is a call flow diagram for a network-level de-registrationprocedure.

FIG. 14 is a call flow diagram for dial tone, digit transmission anddigit analysis for a communication system having a PBX.

FIG. 15 is a call flow diagram for dial tone, digit transmission anddigit analysis for a communication system including a key system (KTS).

FIG. 16 is a call flow diagram for dial tone, digit transmission anddigit analysis for a communication system having another type of PBX.

FIG. 17 is a call flow diagram for dial tone, digit transmission anddigit analysis for a communication system having another type of KTS.

FIG. 18 is a call flow diagram for a successful outgoing call setupwithout PSTN interworking.

FIG. 19 is a call flow diagram for a successful outgoing call setup withPSTN interworking.

FIG. 20 is a call flow diagram for a scenario involving call waiting.

FIG. 21 is a call flow diagram for a scenario involving three-waycalling.

FIG. 22 is a call flow diagram for DTMF tone transmission.

FIG. 23 is a timing diagram of an over-the-air protocol that may be usedin the communication system shown in FIG. 1.

FIG. 24 is a timing diagram of an alternative over-the-air protocol forthe communication system shown in FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a diagram showing an overall system architecture of acommunication system 101 in accordance with a preferred embodiment ofthe present invention. In the system architecture illustrated in FIG. 1,a plurality of telephone stations 102 are connected to a centraltelephone switch 105. It will be understood that telephone stations 102could comprise telephones, modems, fax machines, or other devices thatare capable of communicating over a completed call connection. Thecentral telephone switch 105 will be referred to herein as a “customerpremises equipment” or “CPE.” The CPE 105 may comprise, for example, aprivate-branch exchange (PBX) system or a key system. The design ofvarious types of PBX and key systems is well known in the art.

In the preferred embodiment depicted in FIG. 1, the CPE 105 is connectedto both a public switched telephone network (PSTN) 125 and wirelessaccess communication unit 106 (also referred to occasionally herein, orin the drawings, as a “customer premises radio unit” or “CPRU”). Asdescribed in more detail hereinafter, in a preferred embodiment callsare selectively placed over the PSTN 125 and the wireless accesscommunication unit 106 according to the type of call. The wirelessaccess communication unit 106 communicates over a wireless trunk 108(which comprises a plurality of wireless communication links) to a basestation 109. The base station 109 is connected, along with other basestations 109 in adjacent or nearby geographical regions, to a basestation controller 112. The base station controller 112 is connected toa transcoding unit 115, which is connected to a mobile switching center(MSC) 116. Optionally, the base station controller 112 may be connecteddirectly to the mobile switching center 116, without the intermediarytranscoding unit 115. The mobile switching center 116 is connected tothe PTSN 125.

In addition to being connected to the transcoding unit 115 or,optionally, the MSC 116, the base station controller 112 is alsoconnected to an operations and maintenance center (OMC) 120, which is inturn connected to an operations support system (OSS) 122. The mobileswitching center 116 is connected to a home location register andauthentication center (HLR/AuC) 123 and to the operations support system122, as shown in FIG. 1. The base station 109 may also be connected to alocal management terminal 121.

As further described herein, the invention provides in one aspect forthe transmission of dialed digits (such as DTMF tones) over acommunication path that includes at least one wireless link. At callsetup, dialed digits are transmitted from the wireless accesscommunication unit 106 to the base station 109 as signaling messages.During an active call, dialed digits are transmitted from the wirelessaccess communication unit 106 to the network using GSM DTAP messages toindicate the start and stop of each digit. The DTAP messages are relayedtransparently through the base station 109 and base station controller112 to the mobile switching center 116. Further details relating todigit transmission are described later herein, after a description ofsome of the structure and operation of basic components of a preferredsystem.

In the preferred communication system 101 shown in FIG. 1, calls may beplaced from telephone stations 102 directly over the PSTN 125 (i.e.,over a landline connection), or over the wireless trunk 108 to the PSTN125 by utilizing the wireless access communication unit 106. When a callis to be initiated at one of the telephone stations 102, it may berouted either directly to the PSTN 125 or to the wireless accesscommunication unit 106. The routing of the call may be either based onmanual selection, or accomplished automatically based on the numberdialed, as further described herein. In a preferred embodiment, localtelephone calls are routed directly to the PSTN 125, while long distancetelephone calls are routed through the wireless access communicationunit 106.

Operation of the system shown in FIG. 1 may depend in part on the natureof the CPE 105. As noted previously, the CPE 105 may comprise, forexample, a PBX or a key-type system. In an embodiment where the CPE 105comprises a PBX, the PBX is preferably capable of routing an outgoingcall placed from a telephone station 102 to the PSTN 125 or to thewireless access communication unit 106 based on either an access digitor the telephone number dialed by the user. The user may, for example,dial a certain first digit (e.g., an ‘8’) for access to the wirelessaccess communication unit 106, and a different first digit (e.g.; a ‘9’)for direct LEC access to the PSTN 125. In this manner, the user could,for example, access the wireless access communication unit 106 to makeoutgoing long distance telephone calls, or the PSTN 125 for other typesof outgoing calls. Alternatively, some types of PBXs can be configuredto analyze the dialed number, and to route long distance and localcalls. Utilizing this ability, the PBX can be configured to route longdistance calls through the wireless access communication unit 106 andlocal or emergency calls through the PSTN 125.

In an embodiment where the CPE 105 comprises a key system, the user maymanually select a line (either for the wireless access communicationunit 106 or the PSTN 125) by depressing a key on the telephone deskset.The user could, for example, select the call processing unit 106 foroutgoing long distance calls, and the PSTN 125 for other types ofoutgoing calls. Some key systems can, like certain PBXs, be configuredto analyze the dialed number, and to route a call either to the wirelessaccess communication unit 106 or the PSTN 125 depending on the initialdigits of the call and/or the number of digits dialed. In this manner,the key system can, for example, be configured to route long distancecalls through the wireless access communication unit 106, and local oremergency calls through the PSTN 125.

In alternative embodiments, the system may be configured with lessflexibility but a potentially simpler architecture. For example, thesystem can be configured such that all incoming calls are routeddirectly from the PSTN 125 to the CPE 105, and that all outgoing localcalls (whether voice or data), all outgoing long distance data calls,and all TTY calls for persons with disabilities are also routed directlythrough the PSTN 125. In such an embodiment, the wireless accesscommunication unit 106 would generally provide outgoing long distancevoice communication capabilities.

The CPE 105 is connected to the wireless access communication unit 106across a CPE trunk interface 104. The CPE trunk interface 104 comprisesa plurality of CPE trunks, each of which may comprise, for example,loop-start trunks or ground-start trunks. The design of both loop-starttrunks and ground-start trunks is well known in the art. As is also wellknown to the practitioner in the art, both loop-start trunks andground-start trunks can be supported by the same local area switchingequipment (i.e, the same PBX or KTS).

In an embodiment in which the CPE 105 comprises a PBX, the PBXpreferably has certain operating characteristics. In addition tosupporting loop-start trunks or ground-start trunks (or both) on the CPEtrunk interface 104 between the PBX and the wireless accesscommunication unit 106, the PBX also preferably supports DTMF addresssignaling on the loop-start trunks or ground-start trunks. The PBX maybe configured to route calls through either the PSTN 125 or the wirelessaccess communication unit 106, as described previously, and thereforehas the ability to identify which trunks lead to the PSTN 125 and whichtrunks lead to the wireless access communication unit 106. The PBXpreferably has the ability to specify the order in which the trunkgroups are tried when an outgoing call is placed, and to re-routeoutgoing long-distance calls through the PSTN 125 instead of thewireless access communication unit 106 in case of access problems fromthe wireless access communication unit 106 to the wireless system.

In an embodiment where the CPE 105 comprises a key telephone system(KTS), the KTS preferably has certain operational characteristics. Inaddition to being configured to support loop-start trunks orground-start trunks (or both) on the CPE trunk interface 104 between theKTS and the wireless access communication unit 106, the KTS alsopreferably supports DTMF address signaling on the loop-start trunks orground-start trunks, and has the ability to route calls through eitherthe PSTN 125 or the wireless access communication unit 106, as describedabove. While not essential, the KTS may also be provided withsupplementary call support features and a route selection feature (i.e.,the ability to identify trunk groups leading to the wireless accesscommunication unit 106 and the PSTN 125, and to specify on the KTS theorder in which the trunk groups should be tried). If a route selectionfeature is provided, the KTS should have the ability to re-routeoutgoing long-distance calls through the PSTN 125 instead of thewireless access communication unit 106, in case there are accessproblems from the wireless access communication unit 106 to the wirelesssystem.

The wireless access communication unit 106 acts as the gateway forwireless trunk access to the CPE 105 via the wireless system, andcorrelates the individual CPE trunks with wireless communication linkssuch that calls from the CPE 105 can be completed over a wirelessnetwork. FIG. 6 is a diagram illustrating an embodiment of a wirelessaccess communication unit 605 connected to a CPE 105 (see FIG. 1) acrossa plurality of CPE trunks 602 (in this example, four CPE trunks 602).The wireless access communication unit 605 also is connected over aplurality of wireless communication links (or “pipes”) 609 to a wirelessnetwork and, in particular, to a base station (not shown in FIG. 6). Thewireless access communication unit 605 establishes the wirelesscommunication links 609 and correlates therewith the CPE trunks 602, sothat communication for a particular CPE trunk 602 is carried out over anassigned wireless communication link 609. Users connected to the CPE 105can obtain access to the wireless access communication unit 605 (and,hence, to the wireless network) by being connected through the CPE 105to one of CPE trunks 602. In this manner, a potentially large number ofusers connected to the CPE 105 can have the ability to complete calls tothe wireless network, with the number of users able to make callssimultaneously equaling the number of CPE trunks 602 (and wirelesscommunication links 609) available.

Various components of the communication system shown in FIG. 1 will nowbe described in more detail. In addition, a detailed description of thepreferred system interworking, protocols and related information appearshereinafter, and also appears in copending U.S. patent application Ser.Nos. 08/987,957, 08/988,482, 08/988,546 (now U.S. Pat. No. 6,208,627,issued Mar. 27, 2001), Ser. Nos. 08/988,505, 08/,988,262 (now U.S. Pat.No. 6,097,817, issued Aug. 1, 2000) and Ser. No. 08/987,872 each ofwhich is filed concurrently herewith, and each of which is herebyincorporated by reference as if set forth fully herein.

The wireless access communication unit 106, as noted, acts as thegateway for the CPE 105 to the wireless network, and preferably performsa variety of functions. In a preferred embodiment, the wireless accesscommunication unit 106 performs off-hook detection for outgoing callsand supports provision of a dial tone to the CPE 105 (and thereby to thetelephone station 102 initiating the call). The wireless accesscommunication unit 106 also initiates acquisition of a wirelesscommunication channel (such as an over-the-air time slot, for example,if the wireless network is a TDMA and/or TDD system), and initiates callcontrol procedures. During call establishment, the wireless accesscommunication unit 106 detects dialed address digits (i.e., DTMF tones)and passes the received digits via call control signaling to thenetwork. The wireless access communication unit 106 decides whether tolaunch a normal or emergency call depending upon an end-of-dialingindication received from the base station 109 indicating the type ofcall (based on digit analysis performed at the base station 109). Inaddition, the wireless access communication unit 106 detects off-hooktransitions from the CPE 105, and initiates call release procedurestowards the network in response to an off-hook transition. When a callis completed, the wireless access communication unit 106 provideslandline-transparent control of disconnect procedures for clearinginitiated by the CPE 105. As part of this function, the wireless accesscommunication unit 106 implements the release guard times supported byconventional wireline systems.

In addition to the above functions, the wireless access communicationunit 106 also supports the signaling of DTMF digits during an activecall. As part of this function, the wireless access communication unit106 detects DTMF tones from the CPE 105 during an active call and relaysthe digits to the network via DTAP signaling. Also during a call, thewireless access communication unit 106 may pass call progress tonesreceived from the network transparently over the bearer path to the CPE105. Whenever call progress DTAP signaling is received from the network,the wireless access communication unit 106 converts the call progressDTAP signals into call progress tones towards the CPE 105. The wirelessaccess communication unit 106 may generate reorder tones to the CPE 105when needed, so as to indicate congestion of the wireless network orpermanent signal timer expiry conditions to the CPE 105.

Additionally, the wireless access communication unit 106 also preferablyperforms a number of functions related to bearer processing. Forexample, in a preferred embodiment the wireless access communicationunit 106 performs vocoding for voice communication. In this regard,vocoding includes encoding/compression of speech towards the network anddecoding/de-compression of speech in the reverse direction (i.e.,towards the CPE 105). The wireless access communication unit 106 alsopreferably performs forward error correction (FEC), encryption anddecryption for the bearer voice (with the wireless access communicationunit 106 and transcoding unit 115 being peer-to-peer endpoints forciphering), and echo cancellation functions. For encryption anddecryption, the wireless access communication unit 106 encrypts thebearer data prior to transmission over the air (i.e., over the wirelesstrunk 108), and decrypts bearer data received from the network. Echocancellation functions are supported by the wireless accesscommunication unit 106 so as to suppress the echo potentially generatedtowards the wireless network if, for example, a 2-4 wire hybridstructure is present at the interface with the CPE 105.

In a preferred embodiment, the wireless access communication unit 106 inconjunction with the wireless system supports management and securityfeatures such as call registration, de-registration, userauthentication, ciphering of bearer information, and network managementfunctions. In addition to providing a means for outgoing voice calls,the wireless access communication unit 106 may also support outgoingemergency (i.e., “911”) calls and end-to-end DTMF signaling duringactive calls.

Details of a preferred wireless access communication unit 201 aredepicted in FIG. 2, and of a preferred software structure for thewireless access communication unit 201 in FIG. 3. As shown in FIG. 2,the wireless access communication unit 201 comprises a plurality ofsubscriber ports 203, which are provided for connecting the CPE 105 (seeFIG. 1) to the wireless access communication unit 201 across a trunkinterface (e.g., trunk interface 104 shown in FIG. 1). Each subscriberport 203 can support one call connection over the wireless accesscommunication unit 201, and may comprise, for example, an RJ-11interface. While four subscriber ports 203 are shown in FIG. 2, it willbe understood that the number of subscriber ports 203 may vary dependingupon the particular application or environment in which the wirelessaccess communication unit 201 is deployed. For example, the wirelessaccess communication unit 201 may be configured with only a singlesubscriber port 203, or may have any number of subscriber ports 203limited only by practical considerations such as the number of wirelesscommunication channels generally accessible and available to thewireless communication unit 201. Also, the subscriber ports 203 maycomprise any suitable interface, with an RJ-11 interface being but oneexample of such an interface.

Each subscriber port 203 is connected to an individual line interfaceunit or line card section 205. Thus, the wireless access communicationunit 201 comprises four line card sections 205, one for each subscriberport 203. The line card section 205 provides a physical subscriber lineinterface from the CPE 105 to the wireless access communication unit201, and in addition provides digitizing and data compression functions.

Details of one of the multiple line card sections 205 are shown in FIG.2, with the other line card sections 205 being configured in a similarfashion. The line card section 205 comprises a subscriber interface 207which is connected to one of the subscriber ports 203. The subscriberinterface 207 comprises a subscriber line interface circuit (SLIC) 217,which provides conventional loop interface functions including batteryfeed, overload protection, supervision, and 2-4 wire hybrid. Bothloop-start and ground-start signaling are preferably supported by theline card section 205. The selection between loop-start and ground-startsignaling may be made, for example, by use of a manual toggle switch ordip switch (not shown) located on the wireless access communication unit201, each line card section 205 may be individually configured tointerface with a loop-start or ground-start trunk. The subscriberinterface 207 further comprises a standard CODEC or, alternatively, asubscriber line audio processing circuit (SLAC) 215 which carries outanalog-to-digital and digital-to-analog conversion between the line cardsection 205 and the user station (e.g., telephone station 102 shown inFIG. 1) connected to the subscriber port 203. The CODEC or SLAC 215provides a standard μ-law pulse code modulation (PCM) interface. Thesubscriber interface 207 also comprises a ring generator 216 forgenerating a ringback tone.

A digitized data stream is output from the CODEC or SLAC 215 andprovided across signal line(s) 214 to a vocoder 206, which compressesthe digitized data stream into a compressed data signal. The vocoder 206comprises a relatively high-speed digital signal processor 211(operating at, e.g., a rate of twenty million instructions per second orother suitable rate), along with support modules such as a high-speedstatic random-access memory (SRAM) 212 and an EPROM 213. The vocoder 206preferably provides, as part of its decoding function, an interpolationcapability for deriving predicted speech patterns, so as to handlesituations where, for example, the wireless access communication unit201 detects data frames that contain errors, or else the data framescontain errors that cannot be corrected by forward error correction(FEC). The decoding function of the vocoder 206 also preferably providesa mute capability for silencing the output to the CPE 105 whenbeneficial to do so, such as during control traffic exchanges. Thevocoder 206 outputs a compressed data signal at a rate of, e.g., 8 Kbps,which is sent to a control line card assembly (LCA) 226 located in acontrol section 220. Control section 220 thereby receives fourcompressed data signals, one from each of the line card sections 205.

Each line card section 205 also hosts a subscriber interface module(SIM) 208. The general functions of the SIM 208 are to provide systemsecurity and store subscriber-specific information, including suchthings as subscriber authentication information and subscriber-specificdata. In a preferred embodiment, the SIM function is duplicated for eachCPE trunk supported by the wireless access communication unit 201, aseach CPE trunk may be viewed as a different subscriber by the network.This duplication may be explained with reference to FIG. 6. In FIG. 6, aplurality of CPE trunks 602 are shown connected to the wireless accesscommunication unit 605 (each CPE trunk 602 being connected to asubscriber port 203 shown in the more detailed diagram of FIG. 2). Aseparate SIM 606 is associated with each of the CPE trunks 602. Thus,for four CPE trunks 602, the wireless access communication unit 605comprises four SIMs 606. The wireless access communication unit 605further comprises a plurality of radio interface units 607, one for eachof CPE trunk 602, for the purpose of passing data and other informationto the wireless transceiver (not shown) which handles the physicalwireless communication links 609.

Generally, each subscriber within the communication system requiresunique identification and possibly different system parameters. To theextent that the multiple CPE trunks (corresponding to the multiplesubscriber ports 203 shown in FIG. 2) are viewed by the system asindividual and unique subscribers, each CPE trunk is associated with aunique identifier and, preferably, unique authentication and othersystem parameters, which are implemented at least in part with theseparate SIM 208 used in each line card 205. Thus, for four CPE trunks(corresponding to the four subscriber ports 203 shown in FIG. 2), fourcopies of the SIM 208 are used in the wireless access communication unit201.

The functionality of the SIM 208 may be implemented as one or morenon-removable SIM chips within the wireless access communication unithardware architecture. The SlIM 208 stores within a non-volatile memory(such as a ROM, or non-volatile RAM) subscriber information such as asubscriber identifier. In a preferred embodiment, the subscriberidentifier comprises an international mobile subscriber identity (IMSI)number. In addition to storing the subscriber identifier, the SPA 208also runs an authentication procedure such as, for example, an “A3”and/or “A8” authentication procedure conventionally used in certain GSMapplications. Further details regarding authentication may be found incopending U.S. patent application Ser. No. 08/988,505, previouslyincorporated herein by reference.

The control section 220 of the wireless access communication unit 201provides timing and control for virtually all aspects of the wirelessaccess communication unit 201. The control section 220 comprises aprocessor 225 which may comprise, for example, a 16-bit RISC processor(such as a C165 or C163 processor manufactured by Siemens Corp.) andassociated support modules (i.e., SRAM, flash memory, etc.). Access tothe SIM 208 is initiated by the host processor 225 and controlled andformatted by the control line card assembly (LCA) in the control section220. The processor 225 also coordinates most system activities and movesdata between the various modules.

The processor 225 is connected to the control LCA 226 which, as notedabove, is connected to the vocoder 206 from each of the line cardsections 205. The control LCA 226 is also connected to a radio interfaceline card assembly (RIF LCA) 227. The control LCA 226 provides theinterface between the radio section and the line card section of thewireless access communication unit 201. The control LCA 226 packages andformats data, and coordinates and controls the over-the-air (OTA)protocol. It thereby maintains coordination between up to fourcompressed serial data streams (one from each of the line card sections205) and their respective over-the-air communication channels.

The radio interface LCA 227 is connected to a baseband processor 228,which may include a digital radio ASIC (DRA) 229. The baseband processor228 is connected to a radio section 240. The radio section 240preferably comprises a plurality of antennas 243 which are selectable bya selector 242 which is connected to the control. LCA 226. Signals fromone or more antennas 243 are thereby provided to a radio transceiver 241(possibly including multiple radio receivers, one for each antenna 243).In a preferred embodiment, antenna diversity techniques are utilizedsuch that the wireless access communication unit 201 selects the bestantenna (and/or radio receiver) for each frame of time in which itcommunicates. Various antenna selection techniques are known in the art,or are described in, for example, U.S. patent application Ser. No.08/826,773 filed Apr. 7, 1997, hereby incorporated by reference as ifset forth fully herein.

The wireless access communication unit 201 may be powered either throughan external DC power supply 250 or an on-board battery 251. The battery251 may be used as a reserve power supply, being brought into serviceautomatically if the external DC supply 250 is cutoff or otherwiseunavailable. A power section 221 for the wireless access communicationunit 201 may comprise local voltage regulators to supply required powerto the logic and radio sections, and a switching regulator to supply anyrequisite loop battery voltage.

The wireless access communication unit 201 may be provided with an LED231 or other visual display mechanism(s) to indicate the status of thedevice to an observer. The types of status conditions to be displayedmay include, for example, whether the power is on, whether the device isfunctional (i.e., all self tests have been passed), or whether thedevice is in service (i.e., is currently registered with a basestation).

In operation, compressed serial data is transferred to and from themultiple line cards 205 under the direction of the control LCA 226. Thecontrol LCA 226 places the compressed serial data in a format suitablefor the radio interface LCA 227. It also performs any desired encryptionor adds forward error correction information. The control LCA 226transfers the data to the radio interface LCA 227 which passes the datato the baseband processor 228. The radio interface LCA 227 keeps trackof channel and timing information, and instructs the baseband processor228 to process the data according to the channel and timing parameters.In a preferred embodiment, the baseband processor 228 comprises atransmitter for formulating continuous phase modulated spread-spectrumsignals, or other types of quadrature or related signals, as described,for example, with respect to transmitters shown in U.S. Pat. Nos.5,629,956, 5,610,940 or 5,548,253, all of which are hereby incorporatedherein by reference as if set forth fully herein. At the appropriatetime intervals, as determined by the radio interface LCA 227, thebaseband processor 228 sends the data to the radio section 240 whichconverts the signal to the appropriate transmission frequency andperforms any necessary filtering for transmission over the air. Thefrequency band utilized by the wireless access communication unit 201 isgenerally dictated by the overall communication system within which theunit is deployed. For example, the frequency band may be within the PCSfrequency band of 1930 MHz to 1990 MHZ, or may by any other suitablefrequency band or bands.

Incoming message signals are received by one or more of antennas 243 andsent to the radio transceiver 241 for downconversion and/or filtering asneeded. The downconverted and/or filtered data is then sent to thebaseband processor 228 which demodulates the received signal. In apreferred embodiment, the wireless access communication unit 201transmits and receives messages using a spread spectrum format. In suchan embodiment, the baseband processor 228 preferably comprises a spreadspectrum correlator. A wide variety of spread spectrum correlators areknown in the art, examples of which include embodiments illustrated ordescribed in U.S. Pat. Nos. 5,629,956, 5,610,940, 5,396,515 or5,499,265, each of which is hereby incorporated by reference as if setforth fully herein.

The baseband processor 228 outputs, among other things, a receivedsignal strength indicator (RSSI), which is used by the control LCA 226in selecting the best antenna 243 (and/or radio receiver) for receptionof the incoming signal. After spread spectrum correlation, the basebandprocessor 228 provides a stream of data bits to the radio interface LCA227, which transfers the data to the appropriate line card 205 basedupon the over-the-air communication channel over which the data wasreceived. The data is then processed by the line card 205 and sent tothe CPE 105 via the particular subscriber port 203 connected to the linecard 205.

A diagram of a preferred software structure for the wireless accesscommunication unit 201 is shown in FIG. 3. As shown in FIG. 3, thesoftware of the wireless access communication unit 201 is functionallydivided into two main components, based on the physical interfacessupported by the wireless access communication unit 201. These two maincomponents are referred to in FIG. 3 as the line manager 350 and theover-the-air manager 351.

The line manager 350 generally handles the CPE trunk management andcommunication between the wireless access communication unit 201 and theCPE 105. In addition to CPE trunk management and communication interfacefunctions, the line manager 350 is also responsible for call signaling,DTMF recognition, and transfer of collected DTMF digits to theover-the-air manager 351. The line manager 350 comprises a plurality ofline drivers 303 and a plurality of SIM drivers 304, one line driver 303and one SIM driver 304 for each CPE trunk supported by the wirelessaccess communication unit 201. A single line driver 303 and SIM driver304 collectively comprise a CPE line software component 302.

The over-the-air manager 351 handles the communication interface andlink management to the base station 109 (see FIG. 1). The over-the-airline manager 351 is also responsible for receiving DTMF digits from theCPE 105 (via the line manager 350) and relaying the DTMF digits to thebase station 109 (which ultimately conveys them to the PSTN 125), as setforth in more detail hereinafter. The over-the-air line manager 351 alsoimplements the over-the-air communication protocol, including end-to-endcommunication with various network entities such as the base stationcontroller 112 and mobile switching center 116 (shown in FIG. 1).Exemplary over-the-air communication protocols that may be implementedby the over-the-air manager 351 include, for example, the GSM directapplication transfer part (DTAP) protocol, or the IS-661 over-the-air(“O-Notes”) protocol as described in the OMNI_Notes_RMT Protocols Rev.02.03D (release date Jun. 30, 1997), appearing as a Technical Appendix Afiled herewith, and hereby incorporated by reference as if set forthfully herein. At the physical radio level, the over-the-air manager 351of the wireless access communication unit 201 preferably implements theIS-661 protocol as set forth in the above-referenced OMNI_Notes_RMTProtocols publication, or a variation thereof.

As further illustrated in FIG. 3, the over-the-air manager 351 comprisesa plurality of CPE line link objects 310, one for each CPE trunk (i.e.,subscriber port 203) supported by the wireless access communication unit201. Each CPE line link object 310 provides the signaling resource for asingle CPE line or trunk, and comprises several components whichtogether form a signaling protocol stack. The components of thesignaling protocol stack work together to interface with a CPE line toprovide call management, mobility management and radio resourcefunctionality required to complete a voice call, and the registrationfunctionality required to utilize network resources.

Each CPE line link object 310 comprises a CPE line manager 311, thepurpose of which is to interface with the CPE line software component302 for the appropriate CPE line or trunk. In a preferred embodiment,the CPE line manager interfaces with a GSM call management component 312and a GSM call registration component 313, both of which interface witha GSM mobility management component 314. The GSM mobility managementcomponent 314 interfaces with a protocol adaption (PAL) component 315,which interfaces with an over-the-air state (OTA) machine 316. The OTAstate machine 316 is generally responsible for managing the physicalradio interface, and communicates with the radio transmit/receiverinterface and slot management (RTRX) component 321.

In operation, the CPE line manager 311 signals the GSM mobilitymanagement component 314 to initiate connection establishmentprocedures, as described in more detail hereinafter with respect to thecall flow diagrams appearing in FIGS. 13 through 22. The CPE linemanager 311 also controls transmission of DTMF digits to the network,the enabling of the speech path, generation of ringback tones,generation of a busy tone (in non-PSTN interworking situations), andpassing of on-hook indication to the CPE 105. In addition, the CPE linemanager 311 manages CPE-initiated call clearing as well as normal andemergency call procedures.

The GSM call management component 312, GSM registration component 313,and GSM mobility management component 314 provide a degree of GSMfunctionality relating to call management, registration, and mobilitymanagement, respectively. The protocol adaption component 315 adapts, ifnecessary, the GSM signaling protocol to the over-the-air protocol (suchas, for example, to the IS-661 over-the-air protocol). The OTA statemachine 316 implements the over-the-air protocol and, as noted, managesthe physical radio interface.

In addition to the multiple CPE line link objects 310, the OTA manager351 further comprises a hardware services component 320 which provides aprogramming interface to the hardware (including hardware controlled bythe line drivers 303 and SIM drivers 304) of the wireless accesscommunication unit 201. The OTA manager 351 may comprise a real-timeoperating system. (RTOS) 330, which may be a multi-tasking operatingsystem, as well as a power-on/reset initialization (POST) component 323and a debug port manager 322. The debug port manager 322, if provided,allows access externally to the internal status of the software, andalso permits software downloads.

In addition to the above-described components, the OTA manager 351 alsocomprises an operations, administration and management (OAM) component324. The OAM component runs at the application level, and performs suchfunctions as recognition of faults, creating and sending alarms, andcommunicating with the line manager 350 for call processing data neededin fault detection and alarms. The types of faults or failures monitoredmay include, for example, hardware failures (such as power supplyfailures, radio unit failures, line card failures, and so on), softwarefailures, communication failures, and quality of service failures (e.g.,unsuccessful call attempts per time period, time slot interchangerequests per time period, unsuccessful time slot interchanges per timeperiod, number of dropped calls per time period, channel quality asindicated by bit error rate, and so on), among others. Fault reportingmay be coordinated such that a single fault that causes multiplefailures due to the dependency of the software, hardware and telecomfunctions will result in a single fault being reported.

In one aspect, the functionality of the over-the-air manager 351 used tosupport the wireless access communication unit 201 may be viewed as asubset or modification of the functionality that would be used tosupport a mobile user application. For example, the mobility managementinterface (MMI) software component used in a conventional GSM system tosupport a mobile user is, in the software architecture shown in FIG. 3,replaced with a CPE line manager 311. Another difference over a mobileuser application is that a logical instance of the signaling protocolstack is provided for each CPE line connected to the wireless accesscommunication unit 201 (as opposed to having a single logical instanceof the signaling protocol stack for a mobile user application), and theSIM driver is modified over a mobile user application to accommodatemultiple SIMs (or their logical equivalents) by, for example, theprovision of multiple independent SIM drivers 304. Further, an abilityis added to associate a hardware voice path from the CPE 105 with a basestation communication link. The signaling protocol may also be modified,as further described herein, to support digit analysis by the basestation 109 (see FIG. 1). DSAT and DTA adaptor software componentsconventionally used in certain mobile user applications are not neededby the wireless access communication unit 201, and are therefore notimplemented.

Referring back to FIG. 1, a base station 109 interfaces with thewireless access communication unit 106 to allow access to the PSTN 125.A block diagram of a preferred base station 401 is shown in FIG. 4. Thebase station 401 comprises a number of separate components connectedtogether by a common global bus backplane, as illustrated in FIG. 4.These components include a digital line card 404, an over-the-air (OTA)processor card 405, a power supply module 407, and a plurality of radiocards 406, all of which reside on an electronics module 420. Theelectronics module 420 is connected to an I/O module 421, whichcomprises protection circuitry 403 to prevent such things as damage fromshort circuits. Each radio card 406 is connected via the protectioncircuitry 403, to one of a plurality of antennas 403. The digital linecard 404 is connected, via protection circuitry 403, to the PSTN 125(through base station controller 112 and MSC 116, as shown in FIG. 1)over a backhaul line 430, and possibly to other base stations 109 aswell over other physical connections. The base station 401 may beconnected to a local AC power supply line 425, if available.

In operation, the wireless access communication unit (identified byreference numeral 412 in FIG. 4) transmits over-the-air messages to andreceives over-the-air messages from the base station 401. The multipleantennas 411 and radio cards 406 are used at the base station 401 forachieving antenna diversity. Typically one antenna 411 is selected at agiven time for transmitting or receiving over-the-air signals. If spreadspectrum communication is being used, then the OTA processor card 405may comprise a spread spectrum correlator and other baseband processingcircuitry for correlating a spread spectrum signal received from thewireless access communication unit 412 and converting it to data bits.The OTA processor card 405 transfers data to the digital line card 404,which formats the data and sends it over a backhaul line 430 to the PSTN125 via the other intervening system components (such as the basestation controller 112 and MSC 116). Similarly, the digital line card404 receives data from the PSTN 125, and transfers the data to the OTAprocessor card 405 which formats the data for the over-the-air protocoland transmits the formatted data using a selected radio card 406 andantenna 411.

The primary functions of the radio cards 406 are to transmit and receiveRF data packs, to perform packet data integrity services (e.g., cyclicredundancy checks), and to support antenna diversity algorithms. Theprimary function of the OTS processor card 405 is to move bearer databetween the radio cards 406 and the digital line card 404. The OTAprocessor card 405 also executes operations, administration, managementand provisioning (OAM&P) requests from the digital line card 404,communicates signaling information (using internal base station messagesor “I-Notes”) with the digital line card 404, and communicates signalinginformation (using over-the-air signaling messages or “O-Notes”) withthe wireless access communication unit 412. Various types of signalinginformation and formats therefor (including I-Notes and O-Notes) thatmay be transmitted across or within the base station 401 or other systemcomponents are described in, for example, copending U.S. patentapplication Ser. No. 08/532,466 filed Sep. 22, 1995, hereby incorporatedby reference as if set forth fully herein.

The primary functions of the digital line card 404 are to handle linkaccess procedures for the “D-channel” (LAPD) transport on the backhaulline 430, to exchange bearer data between the OTA processor card 405 andthe network-side backhaul components (such as the base stationcontroller 112), and to multiplex and demultiplex bearer data on thebackhaul line 430. Other primary functions of the digital line card 404include synchronizing the over-the-air bearer frame timing with thetiming on the backhaul line 430 (such as a T1 line), to providetranslation between the OAM&P procedures supported on the network andradio interfaces, to map internal base station messages (e.g., I-Notes)to/from the LAPD transport on the backhaul, and to communicate signalinginformation (using, e.g., signaling I-Notes) with the OTA processor card405.

A preferred high level software architecture for the base station 401 isdepicted in FIG. 5. According to the software architecture shown in FIG.5, the software of the base station 401 is split into two functionalgroups, one functional group relating to the over-the-air functions andthe other functional group relating to the line card functions. Thesetwo main functional groups are shown in FIG. 5 as the OTA manager 502and the line card manager 503, each of which preferably runs on its ownprocessor board. Further details regarding the software architecture forthe base station 401 may be found in the copending patent applicationspreviously incorporated herein by reference.

Various interfaces associated with the base station 401 are showndiagrammatically in FIG. 5 as dotted lines, and include an over-the-airinterface or “O-interface” 560 between the wireless access communicationunit 412 and the base station 401, an internal interface or“I-interface” 561 between the OTA manager 502 and the line card manager503, and a network interface or “N-interface” 562 between the basestation 401 and the network-side backhaul components (such as the basestation controller 112, MSC 116, and PSTN 125 shown in FIG. 1). Furtherinformation regarding these interfaces may be found in copending U.S.patent application Ser. No. 08/532,466, previously incorporated hereinby reference, or in copending U.S. patent application Ser. Nos.08/988,482 and 08/988,546 (now U.S. Pat. No. 6,208,627), previouslyincorporated herein by reference. These interfaces are also shown at anabstract level in FIG. 10, described later herein.

In operation, the base station 401 manages the radio resources for thewireless access communication unit 412, and thereby provides support forthe network side of the wireless trunk 108 (see FIG. 1). A wide varietyof different communication schemes and radio resource protocols may beused. If, for example, the base station 401 implements an IS-661protocol for over-the-air communication, then the base station 401manages the resources necessary to support the wireless communicationchannels between the wireless access communication unit 412 and the basestation 401, including time slots and spread spectrum codes. The basestation 401 also provides multiplexing functions for the transfer ofdata to and from the backhaul line 430 providing the connection to thePSTN 125. The base station 401 may, for example, multiplex data over aT1 (or fractional T1) backhaul line 430 to the base station controller112, which, as noted, pipes the data to and from the PSTN 125 via theMSC 116.

Protocol signaling over the N-Interface 562, which connects the basestation 401 (or 109 in FIG. 1) to the base station controller 112 (seeFIG. 1), may be transported using the Q.921 LAPD protocol. Protocolsignaling over the O-Interface 560, which connects the base station 401to the wireless access communication unit 412, may be accomplished usingover-the-air signaling messages (“O-Notes”) according to the IS-661protocol. The O-Notes may be transmitted along with bearer data inIS-661 RF packets.

The base station 401 connects and manages radio and terrestrial bearerchannels for call-related features, and supports system administrationvia OAM&P controlled by the system operator through the operationsmanagement center 120 (see FIG. 1). As part of its radio resourcemanagement functionality, the base station 401 supports outgoing voicecalls (normal and emergency) from the wireless access communication unit412. Incoming pages to the wireless access communication unit 412 mayoptionally be supported by the base station 401.

Among its other radio resource management functions, the base station401 manages mapping of the radio channels (including the wirelesscommunication channels of the wireless trunk 108) to the terrestrial(i.e., backhaul) channels. The base station 401 also provides, throughits OAM&P functionality, support for administrative state changes,configuration, provisioning of the radio resources, fault management andalarm management for the radio resources. With regard to terrestrialresource management, the base station 401 manages and allocates thebackhaul channels (such as T1 time slots) over the backhaul line 430.The base station 401 indicates backhaul channel allocation to the basestation controller 112 through signaling messages.

In terms of call control support, the base station 401 is involved inestablishing, maintaining and tearing down outgoing voice calls receivedfrom the wireless access communication unit 412. Preferred call flowspertaining to such functions are shown in, e.g., FIGS. 14 through 19,and described in more detail hereinafter. The base station 401 alsorelays DTMF signaling from the end user to the PSTN 125, if necessary,during an active telephone call. This signaling is relayed transparentlythrough the base station 401, and is supported by the I-interface andN-interface transport procedures. The base station 401 also providesdigit analysis for outgoing telephone calls.

Referring again to FIG. 1, the base station 109 connected to the basestation controller 112 over an interface such as an N-interface (such asthe N-interface 562 described previously with respect to FIG. 5). Data(including signaling messages and bearer traffic) are passed between thebase station 109 and the base station controller 112 across theN-interface. A preferred base station controller 112 may be viewed inone aspect as a base station subsystem controller that is used formanaging one or more base stations 109. A primary responsibility of thebase station controller 112 is to provide an interface between the MSC116 and the radio access subsystem (i.e., the system componentsresponsible for establishing and maintaining the physical radiochannels). In a preferred embodiment, the base station controller 112incorporates aspects of the IS-661 communication protocol and the GSMcommunication protocol, thereby using what may be referred to as a“hybrid” protocol. Details of a preferred communication protocol may befound in, for example, copending U.S. patent application Ser. Nos.08/988,482and 08/98 8,546 (now U.S. Pat. No. 6,208,627) both previouslyincorporated herein by reference. In an alternative embodiments, thebase station controller 112 may be implemented using the IS-661 protocolin its entirety, or the GSM communication protocol in its entirety.

Call control messages and procedures run end-to-end between the wirelessaccess communication unit 106 and the MSC 116, and are relayedtransparently through the base station controller 112. In one aspect,the base station controller 112 provides a signaling path between thewireless access communication unit 106 and the MSC 116 to carry out callcontrol signaling.

In a preferred embodiment, the base station controller 112 transmits andreceives information to the transcoding unit 115, shown in FIG. 1. Thetranscoding unit 115 in one aspect comprises a base station subsystem(BSS) entity located, in one embodiment, between the base stationcontroller 112 and the MSC 116. Preferably, the transcoding unit 115 isunder management control of the base station controller 112, but isphysically located on the premises of the MSC 116, thereby allowing thebase station controller 112 to be remotely located from the site of theMSC 116. The transcoding unit 115 comprises a number of transcoding unitshelves, operating independently of one another but under the control ofthe base station controller 112. In a preferred embodiment, eachtranscoding unit shelf supports up to 92 bearer channels. Thetranscoding unit 115 generally provides the network side processing ofkey functions on the bearer path. This processing may include, forexample, speech transcoding, network-side forward error correction(FEC), and network-side enciphering and deciphering of bearer voice.

FIG. 9 is a high level diagram illustrating a preferred breakdown ofbearer path functions performed at the wireless access communicationunit 106, the base station 109, and the base station controller 112and/or transcoding unit 115. As shown in FIG. 9, the wireless accesscommnunication unit bearer path functions 901 include voice encoding anddecoding 911, forward error correction (FEC) 912, encryption anddecryption 913, and tone generation 914. The speech encoding/decoding,encryption/decryption and FEC functions performed in the wireless accesscommunication unit 106 are mirrored in the base station controller 112and/or transcoding unit 115.

Referring again to FIG. 1, the transcoding unit 115 is connected to themobile switching center (MSC) 116, which is connected to the PSTN 125.The MSC 116 is a cellular switch that acts as an interface between thebase station subsystem (BSS) and the PSTN 125, and acts as the gatewayto the long-distance network. The MSC 116 has telephone exchangecapabilities including call setup, routing selection, switching betweenincoming and outgoing channels, control of communications, and releaseof connections. In addition, the MSC 116 performs its functions whiletaking into account mobility management aspects of the subscriber,including authentication, ciphering, radio resource management, andlocation register updating procedures. The MSC 116 also allows thewireless access communication unit 106 interworking to the PSTN 125. TheMSC 116 may be part of a digital multiplex system (DMS) “super-node”based switching system, capable of providing the switching functions ina cellular network. Also, the visitor location register (VLR) ispreferably co-located and integrated with the MSC 116.

Certain features relating to voice call establishment and maintenancewill now be described in more detail, with reference to the interactionamong various components of a communication system in which the wirelessaccess communication unit 106 is deployed. Further details regarding thevarious interfaces between the system components is providedhereinafter.

For “outgoing” voice call establishment initiated by the CPE 105, thewireless access communication unit 106 handles acquisition of anover-the-air communication channel, mobility management connectivity,and call setup, and in addition is preferably capable of handlingvarious error or exception conditions. When the wireless accesscommunication unit 106 detects a trunk seizure by the CPE 105, thewireless access communication unit 106 marks the CPE trunk as “busy” andissues a dial tone (assuming that it is able to communicate with a basestation 109). In parallel, the wireless access communication unitinitiates an over-the-air communication channel acquisition procedure.The dial tone is removed when the wireless access communication unit 106detects the first dialed digit from the CPE 105, or if it detects anon-hook from the CPE 105 prior to receiving any digits therefrom.

On receiving a trigger from the CPE 105 to set up an outgoing call orperform a registration, the wireless access communication unit 106attempts to acquire an over-the-air communication channel. In certainwireless systems the acquisition of an over-the-air communicationchannel is accomplished by interacting with a control channel of thewireless system. In certain types of TDMA systems, the channelacquisition process may entail acquiring a time slot in a time frameestablished by the base station 109. Acquisition of a time slot may becarried out, for example, according to a handshake protocol described inmore detail in U.S. Pat. No. 5,455,822, assigned to the assignee of thepresent invention, and hereby incorporated by reference as if set forthfully herein.

If acquisition of an over-the-air communication channel is successful,then the wireless access communication unit 106 proceeds with digittransmission and analysis. On detecting the first dialed digit, thewireless access communication unit 106 removes the dial tone andinitiates a digit analysis procedure. In a preferred embodiment, digitsare relayed from the wireless access communication unit 106 as they arereceived after the over-the-air communication channel has beenestablished, and digit analysis is performed at the base station 109.The base station 109 stores the digits and analyzes them, determiningthe type of call and the end of the dialing sequence. Examples oftechniques for digit analysis by a base station are further described incopending U.S. patent application Ser. No. 08/676,975 filed Jun. 8,1996, hereby incorporated by reference as if set forth fully herein.

In an illustrative embodiment, the base station 109 analyzes the digitsas follows. If the base station 109 detects the digit pattern “X11,”where “X” is a “4” or a “9”, it will consider dialing to be complete. Ifthe digit sequence is “911,” the base station 109 marks the call type asan emergency call. Any other type of call is marked as a normal call. Ifthe first three digits are not “411” or “911,” then the base station 109continues to receive digits, and uses a dialing-complete timeout period(of, e.g., four seconds) to detect the end of dialing. To implement thedialing-complete timeout period, a dialing timer is activated when thefirst digit is received by the base station 109, and is reset each timea new digit is received. When the dialing timer expires, the basestation 109 considers dialing to be complete.

On determining that the dialing sequence is complete, the base station109 issues a trigger to the wireless access communication unit 106 tocontinue with call establishment, including mobility managementconnection establishment and call setup. This trigger also indicates thetype of call (i.e., normal versus emergency).

Several types of exceptions or errors may occur in the attempt toestablish a communication path from the user (i.e., telephone station102) to the base station 109. For example, if the wireless accesscommunication unit 106 is unable to communicate with the base station109, then the wireless access communication unit 106 will not generate adial tone. Instead, it will issue a reorder tone to the user via the CPE105. If no digit is received by the wireless access communication unitfor a predetermined timeout period (e.g., 16 seconds) after the trunkseizure is recognized by the wireless access communication unit 106,then it applies permanent signal treatment on the trunk (i.e., treats itas an extended off-hook situation), as further described below. If thedialing from the user is incomplete, or if the dialed number is invalid,then the MSC 116 takes appropriate action. In such situations, the basestation 109 generally detects end-of-dialing and triggers the wirelessaccess communication unit 106 to set up the call. The incomplete orinvalid digit sequence is then filled into a DTAP Setup message by thebase station 109 and sent to the MSC 116. The digit analysis performedat the MSC 116 detects the exception condition, causing the MSC 116 toreturn a DTAP Release Complete message to the wireless accesscommunication unit 106, indicating that the dialed number is invalid.

Operation of preferred embodiments of the invention will now bedescribed in more detail, with reference as appropriate to the call flowdiagrams depicted in FIGS. 12 through 22.

In accordance with a preferred embodiment of the invention as depictedin FIG. 1, the wireless access communication unit 106 provides thecapability to establish, maintain and tear down normal outgoing voicecalls through a GSM-based segment that provides connectivity to the longdistance functionality of the PSTN 125. The wireless accesscommunication unit 106 and other system components provide wirelinetransparency to a CPE 105 by supporting standard signaling functions onthe CPE interface, including trunk supervisory signaling, addresssignaling, and provision of call progress tones to the CPE 105.

As part of the initialization procedure after power-up, and preferablyperiodically thereafter, the wireless access communication unit 106registers with a nearby base station 109 and also with the PSTN 125. Inthis context, registration may generally be described as the process bywhich a subscriber (i.e., a CPE trunk 602) connected to the wirelessaccess communication unit 106 identifies itself to the network. Sinceeach CPE trunk connected to the wireless access communication unit 106is looked upon by the network as an individual subscriber, theregistration procedure is typically carried out on behalf of anindividual CPE trunk, and may need to be repeated for multiple CPEtrunks.

FIG. 12 is a call flow diagram illustrating a network-level registrationprocedure. As a first step in the procedure illustrated in FIG. 12, thewireless access communication unit 106 acquires a wireless communicationchannel (e.g., a time slot in a TDMA or TDD system, or a frequencychannel in an FDD system, or other defined channel) to a nearby basestation 109. The wireless communication channel is acquired according tothe particular protocol utilized by the wireless system. The wirelessaccess communication unit 106 then performs a network-level registrationprocedure, according to the particular registration protocol utilized bythe system. The registration procedure may involve, for example, alocation updating procedure on the A-interface. The wireless accesscommunication unit 106 performs network-level registration at regularintervals thereafter, with periodicity controlled by the networkinfrastructure. The wireless access communication unit 106 may alsoperform network-level registration if it starts communicating through abase station 109 in a different location area from the base station withwhich it had been previously communicating. After registration, thewireless communication channel is surrendered, and the MSC 116 initiatesa resource release procedure, as illustrated in FIG. 12.

In addition to network-level registration, the wireless accesscommunication unit 106 may also perform periodic registration with thebase station 109 at regular intervals, with a periodicity controlled bythe base station 109 and/or configurable through OAM&P. For eachregistration attempt, the wireless access communication unit 106acquires a wireless communication channel, registers, and thensurrenders the wireless communication channel, unless a call is inprogress. If a call is in progress, the wireless communication unit 106need not acquire a new channel, but can, if possible under theparticular wireless protocol, send registration information over theexisting communication channel. In addition to periodic base-levelregistration, the wireless access communication unit 106 also performsinitial registration with a base station 109 when it startscommunicating through a base station different from but in the samelocation area as a base station with which it was previouslycommunicating.

De-registration is performed by the system on behalf of each CPE trunkconnected to the wireless access communication unit 106 when thewireless access communication unit 106 is powered off. FIG. 13 is a callflow diagram illustrating a network level de-registration procedure. Asa first step in the procedure illustrated in FIG. 13, the wirelessaccess communication unit 106 acquires a wireless communication channel(e.g., a TDMA time slot) to a nearby base station 109. The wirelesscommunication channel is acquired according to the particular RFprotocol utilized by the wireless system. The wireless accesscommunication unit 106 then performs a network-level de-registrationprocedure, such as an IMSI detach procedure, according to the particularprotocol utilized by the system. After de-registration, the wirelesscommunication channel is surrendered, and the MSC 116 initiates aresource release procedure, as illustrated in FIG. 13.

After registration by the wireless access communication unit 106,outgoing calls may be placed to the PSTN 125 via the CPE 105, wirelessaccess communication unit 106 and base station subsystem. FIGS. 14through 19 are call flow diagrams illustrating dial tone, digittransmission, digit analysis and call setup for outgoing calls undervarious types of CPE embodiments, including PBXs and KTSs with differentlevels of routing intelligence. FIG. 14, for example, is a call flowdiagram illustrating dial tone, digit transmission and digit analysisfor a CPE 105 embodied as a “dumb” PBX—i.e., a PBX without the abilityto route calls based on analysis of the dialed number. As shown in FIG.14, the user 102 (e.g., a telephone station, as shown in FIG. 1) goesoff-hook, sending an off-hook stimulus to the CPE 105 (i.e., the PBX).Upon detecting the off-hook signal, the PBX 105 issues a dial tone tothe user 102. The user 102 then dials an access code (i.e., apredetermined digit, such as ‘8’) to access the wireless trunk offeredby the wireless access communication unit 106. Upon detecting the accesscode digit, the PBX 105 removes the dial tone and seizes a trunkconnected to the wireless access communication unit 106.

On detecting seizure of a trunk, the wireless access communication unit106 issues a secondary dial tone to the user 102. The secondary dialtone is delivered via the PBX 105 to the user 102. In parallel toapplying the secondary dial tone, the wireless access communication unit106 commences acquisition of an over-the-air communication channel. In aTDMA or TDD system, for example, this step in the procedure generallyentails seizing an over-the-air time slot.

Upon detecting the dial tone, the user 102 starts dialing the digits ofthe party to be called. The wireless access communication unit 106detects the first digit, after which it removes the secondary dial tone.If acquisition of the over-the-air communication channel has not beencompleted by this time, the wireless access communication unit 106stores the received digits in a temporary buffer.

After it successfully acquires an over-the-air communication channel, asshown in FIG. 14, the wireless access communication unit 106 sends acontrol traffic service request (CT-SRQ) message to the base station 109requesting service from the digit analysis application in the basestation 109. The base station 109 commences the digit analysisapplication, and returns a control traffic acknowledgment (CT-ACK)message to the wireless access communication unit 106. The wirelessaccess communication unit 106 then transmits the digits received fromthe user 102 to the base station 109 one-by-one as they are receivedfrom the user 102. Each digit is sent as part of a control traffictransport (CT-TRA) message. The value of each digit may be indicated bya field of, e.g., four bits in the CT-TRA message. The base station 109stores each received digit. After all address digits have been receivedat the base station 109, the base station 109 detects that the dialingsequence is complete (according to its digit analysis), and returns acontrol traffic transport (CT-TRA) message to the central callprocessing unit 106, with a message content indicating that dialing iscomplete. The wireless access communication unit 106 is then able toproceed with the launching of the call.

FIG. 15 is similar to FIG. 14, but illustrates dial tone, digittransmission and digit analysis for a CPE 105 embodied as a “dumb”KTS—i.e., a key type system without the ability to route calls based onanalysis of the dialed number. As shown in FIG. 15, the user 102 firstselects an outgoing line to the wireless access communication unit 106.The user 102 then goes off-hook, sending an off-hook stimulus to the CPE105 (i.e., the KTS). Upon detecting the off-hook signal, the CPE 105seizes a trunk connected to the wireless access communication unit 106.The wireless access communication unit 106 detects the trunk seizure,and in response issues a dial tone to the user 102. In parallel withapplying the dial tone, the wireless access communication unit proceedsto acquire an over-the-air communication channel. In a TDMA or TDDsystem, this step generally entails seizing an over-the-air time slot.

When the user 102 detects the dial tone, the user 102 starts dialing thedigits of the party to be called. After detecting the first digit, thewireless access communication unit 106 removes the dial tone. Ifacquisition of the over-the-air communication channel has not beencompleted by this time, the wireless access communication unit 106stores the digits in a temporary buffer.

When it successfully acquires an over-the-air communication channel, thewireless access communication unit 106 sends a control traffic servicerequest (CT-SRQ) message to the base station 109, as shown in FIG. 15,requesting service from the digit analysis application in the basestation 109. The base station 109 commences the digit analysisapplication, and returns a control traffic acknowledgment (CT-ACK)message to the wireless access communication unit 106. The wirelessaccess communication unit 106 then transmits the digits received fromthe user 102 to the base station 109 one-by-one as they are receivedfrom the user 102. Each digit is sent as part of a control traffictransport (CT-TRA) message, as described with respect to FIG. 14. Thebase station 109 stores each received digit. After all address digitshave been received at the base station 109, the base station 109 detectsthat the dialing sequence is complete (according to its digit analysis),and returns a control traffic transport (CT-TRA) message to the centralcall processing unit 106, with a message content indicating that dialingis complete. The wireless access communication unit 106 is then able toproceed with the launching of the call.

FIG. 16, in a fashion similar to FIGS. 14 and 16, illustrates dial tone,digit transmission and digit analysis, but for a CPE 105 embodied as aPBX system which has sufficient built-in intelligence to route callsbased on analysis of the dialed number. As shown in FIG. 16, the user102 first goes off-hook, sending an off-hook stimulus to the CPE 105(i.e., the PBX). Upon detecting the off-hook signal, the CPE 105 issuesa dial tone to the user 102. The user 102 then dials an access code(i.e., a predetermined digit, such as ‘8’ or ‘9’) to access an outsideline. Upon detecting the access code digit, the CPE 105 removes the dialtone and starts digit analysis. On detecting that the dialed number isthe predetermined digit of the access code, the CPE 105 issues asecondary dial tone to the user 102.

The user 102 then starts dialing the digits of the party to be called.Upon detecting the first digit from the user 102, the CPE 105 removesthe dial tone and starts digit analysis. After all the digits have beenreceived by the CPE 105, the CPE 105 determines from its digit analysisthat a complete telephone number has been dialed. The CPE 105 alsodetermines from its digit analysis whether or not the call is longdistance (e.g., the first digit of the call to be placed following theaccess code is a ‘1’), and if the call is long distance seizes a trunkconnected to the wireless access communication unit 106. If the call isnot long distance, the CPE 105 routes the call directly to the PSTN 125.

Upon detecting seizure of a CPE trunk, the wireless access communicationunit 106 issues a secondary dial tone to the user 102. This secondarydial tone is muted by the CPE 105 on the user side—i.e., it is notpassed along to the user 102. In parallel with applying the secondarydial tone, the wireless access communication unit 106 proceeds toacquire an over-the-air communication channel. In a TDMA or TDD system,for example, this step generally entails seizing an over-the-air timeslot. When the secondary dial tone is detected by the CPE 105, the CPE105 begins to outpulse to the wireless access communication unit 106 thedigits earlier received from the user 102 as DTMF tones. Upon detectingthe first digit (i.e., DTMF tone), the wireless access communicationunit 106 removes the secondary dial tone. If acquisition of theover-the-air communication channel has not been completed by this time,the wireless access communication unit 106 stores the digits in atemporary buffer until such time as a wireless communication channel isobtained.

After it successfully acquires an over-the-air communication channel,the wireless access communication unit 106 sends a control trafficservice request (CT-SRQ) message to the base station 109 requestingservice from the digit analysis application in the base station 109. Thebase station 109 commences the digit analysis application, and returns acontrol traffic acknowledgment (CT-ACK) message to the wireless accesscommunication unit 106. The wireless access communication unit 106 thentransmits the digits received from the user 102 to the base station 109one-by-one as they are received from the user 102. Each digit is sent aspart of a control traffic transport (CT-TRA) message. The base station109 stores each received digit. After all address digits have beenreceived at the base station 109, the base station 109 detects that thedialing sequence is complete, and returns a control traffic transport(CT-TRA) message to the central call processing unit 106, with a messagecontent indicating that dialing is complete. The wireless accesscommunication unit 106 is then able to proceed with the launching of thecall.

FIG. 17 is similar to FIGS. 14, 15 and 16, but illustrates dial tone,digit transmission and digit analysis for a CPE 105 embodied as a keytype system (KTS) which has sufficient built-in intelligence to routecalls based on analysis of the dialed number. As shown in FIG. 17, theuser 102 first goes off-hook, sending an off-hook stimulus to the CPE105 (i.e., the KTS). Upon detecting the off-hook signal, the CPE 105issues a dial tone to the user 102. The user 102 then starts dialing thedigits of the party to be called. Upon detecting the first digit fromthe user 102, the CPE 105 removes the dial tone and starts digitanalysis.

After all the digits have been received by the CPE 105, the CPE 105determines from its digit analysis that a complete telephone number hasbeen dialed. The CPE 105 also determines from its digit analysis whetheror not the call is long distance (e.g., the first digit dialed is a‘1’), and if the call is long distance seizes a trunk connected to thewireless access communication unit 106. If the call is not longdistance, the CPE 105 routes the call directly to the PSTN 125.

When a trunk is seized, the wireless access communication unit 106issues a secondary dial tone to the CPE 105. This secondary dial tone ismuted by the CPE 105 on the user side—i.e., it is not passed to the user102. In parallel with applying the secondary dial tone, the wirelessaccess communication unit 106 proceeds to acquire an over-the-aircommunication channel. In a TDMA or TDD system, this step generallyentails seizing an over-the-air time slot. When the secondary dial toneis detected by the CPE 105, the CPE 105 begins to outpulse the digitsearlier received from the user 102 to the wireless access communicationunit 106. Upon detecting the first digit, the wireless accesscommunication unit 106 removes the secondary dial tone. If acquisitionof the over-the-air communication channel has not been completed by thistime, the wireless access communication unit 106 stores the digits in atemporary buffer.

After it successfully acquires an over-the-air communication channel,the wireless access communication unit 106 sends a control trafficservice request (CT-SRQ) message to the base station 109 requestingservice from the digit analysis application in the base station 109. Thebase station 109 commences the digit analysis application, and returns acontrol traffic acknowledgment (CT-ACK) message to the wireless accesscommunication unit 106. The wireless access communication unit 106 thentransmits the digits received from the user 102 to the base station 109one-by-one as they are received from the user 102. Each digit is sent aspart of a control traffic transport (CT-TRA) message. The base station109 stores each received digit. After all address digits have beenreceived at the base station 109, the base station 109 detects that thedialing sequence is complete, and returns a control traffic transport(CT-TRA) message to the central call processing unit 106, with a messagecontent indicating that dialing is complete. The wireless accesscommunication unit 106 is then able to proceed with the launching of thecall.

If the wireless access communication unit 106 issues a dial tone (or asecondary dial tone) and does not receive digits from the CPE 105 withina preset amount of time, a dial timeout condition will occur. In such acase, the wireless access communication unit 106 releases anyover-the-air communication channel that it may have seized and issuespermanent treatment to the user (i.e., preforms a de-registrationprocedure, if necessary, and causes the MSC 116 to release any resourcesallocated for the call).

FIGS. 18 and 19 are call flow diagrams illustrating successful callsetup procedures in two scenarios. FIG. 18 illustrates a call flow for asuccessful CPE-originated normal (i.e., non-emergency) call setupsequence, with non-PSTN interworking at the MSC 116. As depicted in FIG.18, provision of the dial tone, transmission of digits and digitanalysis is carried out according to any of the scenarios illustrated inthe call flow diagrams of FIGS. 14 through 17. In each instance the callflow terminates with an end of dialing indication from the base station109 to the wireless access communication unit 106. Upon receiving theend of dialing indication from the base station 109, the wireless accesscommunication unit 106 initiates a mobility management connectionestablishment procedure for a normal call. This procedure results in anSCCP link being established for the call across the A-interface(assuming a GSM system), and further results in a mobility managementconnection being set up with the MSC 116 for handling the call. Part ofthis procedure may, if desired, entail authentication and cipher modesetting procedures for the call.

After completion of the mobility management connection procedure, thewireless access communication unit 106 sends a direct transferapplication part (DTAP) Setup message to the base station 109, asillustrated in FIG. 18. The DTAP Setup message contains an empty calledparty address field, and is directed towards the MSC 116. The basestation 109 intercepts the DTAP Setup message and fills in the calledaddress field with the digits received from the wireless accesscommunication unit earlier during the digit analysis step. The basestation 109 then forwards the DTAP Setup message, via the base stationcontroller 112, to the MSC 116. The MSC 116 acknowledges the receipt ofthe DTAP Setup message by sending a DTAP Call Proceeding message to thewireless access communication unit 106, as illustrated in FIG. 18.

A bearer resource assignment procedure is then executed on eachinterface of the wireless fixed-access system, starting from theA-interface 571 and progressing to the O-interface 560. The bearerresource assignment procedure results in bearer channels being assignedon the A-interface 571, N-interface 562 and O-interface 560, and aswitched connection being set up through the base station controller112.

After the bearer resource assignment procedure is complete, the MSC 116sends a DTAP Alerting message to the wireless access communication unit106. The wireless access communication unit 106 provides a ringback toneto the user 102, via the inband path through the CPE 105 (i.e., the PBXor KTS, or other similar system). When the called party answers thecall, the MSC 116 sends a DTAP Connect message to the wireless accesscommunication unit 106. At that point the wireless access communicationunit 106 attaches its speech path and removes the ringback tone to theuser 102. The wireless access communication unit 106 responds to the MSC116 with a DTAP Connect Acknowledgment message, and the call is then ina conversation state.

FIG. 19, like FIG. 18, illustrates a call flow for a successfulCPE-originated normal call setup sequence, but with PSTN interworking atthe MSC 116. As depicted in FIG. 19, provision of the dial tone,transmission of digits and digit analysis is carried out according toany of the scenarios illustrated in the call flow diagrams of FIGS. 14through 17. Upon receiving an end of dialing indication from the basestation 109, the wireless access communication unit 106 initiates amobility management connection establishment procedure for a normalcall. Similar to the call flow of FIG. 18, this procedure results in anSCCP link being established for the call across the A-interface(assuming a GSM system), and further results in a mobility managementconnection being set up with the MSC 116 for handling the call. Part ofthis procedure may, if desired, entail authentication and cipher modesetting procedures for the call.

After completion of the mobility management connection procedure, thewireless access communication unit 106 sends a DTAP Setup message to thebase station 109. The DTAP Setup message contains an empty called partyaddress field, and is directed towards the MSC 116. The base station 109intercepts the DTAP Setup message and fills in the called address fieldwith the digits received from the wireless access communication unitearlier during the digit analysis step. The base station 109 thenforwards the DTAP Setup message, via the base station controller 112, tothe MSC 116. The MSC 116 acknowledges the receipt of the DTAP Setupmessage by sending a DTAP Call Proceeding message to the wireless accesscommunication unit 106, as illustrated in FIG. 19. A bearer resourceassignment procedure is then executed on each interface of the wirelessfixed-access system, starting from the A-interface and progressing tothe O-interface, similar to the call flow of FIG. 18. The bearerresource assignment procedure results in bearer channels being assignedon the A-interface, N-interface and O-interface, and a switchedconnection being set up through the base station controller 112.

After the bearer resource assignment procedure is complete, the MSC 116sends a DTAP Progress message to the wireless access communication unit106, indicating interworking with the PSTN 125. The wireless accesscommunication unit 106 attaches its speech path at this point. Thenetwork senses the ringback tone over the connected speech path, and theringback tone is relayed by the wireless access communication unit 106to the user 102, via the CPE 105 (i.e., the KTS or PBX, or other similarsystem). When the called party answers the call, the network removes theringback tone. The MSC 116 sends a DTAP Connect message to the wirelessaccess communication unit 106. The wireless access communication unit106 responds with a DTAP Connect Acknowledgment message, and the callthen moves to a conversation state.

In either call flow scenario depicted in FIG. 18 or 19, if the calledparty is busy, the call will generally be rejected. In the case ofnon-PSTN interworking, a busy tone is sent from the wireless accesscommunication unit 106 to the user 102 in response to a DTAP Disconnectmessage from the MSC 116, and a DTAP release procedure is initiated.When an on-hook signal is detected from the user 102, the wirelessaccess communication unit 106 initiates a call resource releaseprocedure. In the case of PSTN-interworking, the busy tone is sent fromthe PSTN 125. When the CPE 105 detects an on-hook signal from the user102, it sends a disconnect message to the wireless access communicationunit 106, which then initiates a DTAP release procedure followed by acall resource release procedure.

In the case of ISDN interworking on the long-distance network interface,the wireless access communication unit 106 generates the appropriatecall progress tones to the CPE 105 based on DTAP signaling received fromthe MSC 116. Such call progress tones include busy tones and ringbacktones, for example. In case of PSTN interworking, these call progresstones are generated by the PSTN 125 and passed inband to the wirelessaccess communication unit 106, which relays them to the CPE 105. Thedial tone is always generated by the wireless access communication unit106. Also, a reorder tone may be generated by the wireless accesscommunication unit 106 during congestion conditions or as part ofpermanent treatment.

FIGS. 20 through 22 are call flow diagrams depicting various callscenarios. FIG. 20 illustrates a call flow for a call waiting situationduring an active call. FIG. 21 is a call flow diagram illustrating athree-way call setup scenario. Details of these two calf flow diagramsare provided in the copending patent applications previouslyincorporated by reference herein.

The wireless access communication unit 106 supports transmission of DTMFtones during an active call, as may be described with respect to FIG.22. At a general level, in the “forward” direction, the wireless accesscommunication unit 106 detects DTMF tones generated by the CPE 105 andconverts these tones into DTAP signaling towards the MSC 116. The MSC116, upon receiving the DTAP DTMF signaling messages, re-generates theDTMF tones towards the PSTN 125. In the “reverse” direction, DTMF tonesignaling 00during an active call in such a manner is not generallysupported by current GSM protocols.

FIG. 22 illustrates a DTMF signaling procedure during an active callfrom the CPE 105 to the PSTN 125. On detecting a DTMF tone from the CPE105 which exceeds a predefined minimum DTMF timeout period (e.g., 20milliseconds), the wireless access communication unit 106 sends a DTAPStart DTMF message to the MSC 116. The DTAP Start DTMF message indicatesthat a digit is being sent. When the MSC 116 receives this message, itre-generates the DTMF tone towards the network, and returns a DTAP StartDTMF Acknowledgment message to the wireless access communication unit106.

When the wireless access communication unit 106 detects the DTAP StartDTMF Acknowledgement message, it sends a DTAP Stop DTMF message to theMSC 116. Upon receiving the DTAP Stop DTMF message, the MSC stop sendingthe DTMF tone towards the network. The MSC 116 returns a DTAP Stop DTMFAcknowledgment message to the wireless access communication unit 106.The procedure is repeated for each DTMIF tone sent by the CPE 105.

The DTAP Start DTMF message and DTAP Stop DTMF message are both messagessupported by existing GSM protocol. The wireless access communicationunit 106 makes use of the DTAP Start DTMF message and DTAP Stop DTMFmessage to transfer information relating to DTMF tones during an activecall, in a transparent manner to the base station 109 and base stationcontroller 112. The DTMF tones can thereby be related across thewireless communication channel and regenerated at the MSC 116 beforebeing relayed to the network.

Both normal and emergency calls can be handled by the preferredcommunication system of FIG. 1. Emergency calls (i.e., “911” calls) arepreferably routed by the CPE 105 directly to the PSTN 125. This may beaccomplished in the same manner other calls are routed. For example, theuser may dial a PSTN access code for an emergency call (in the case of aPBX), or may select a PSTN trunk from the desksets (in the case of aKTS). Alternatively, the CPE 105 can be configured to route emergencycalls to a PSTN trunk by analyzing the received digits. It maynevertheless be desirable to provide the wireless access communicationunit 106 with the capability to establish, maintain and tear downemergency calls if it receives a trigger to initiate such a call. Thewireless access communication unit 106 may perform these emergency calloperations using a GSM-based segment.

Further details regarding some of the interfaces, signaling techniquesand protocols will now be described.

The “O-interface” 560 is a wireless connection preferably comprising oneor more wireless, over-the-air communication channels, each channelpreferably (but not necessarily) including a forward communication linkand a reverse communication link to support full duplex communication.The over-the-air communication channel(s) of the O-interface 560 may beimplemented according to any of a variety of different multiple-accesscommunication protocols, including protocols utilizing time divisionmultiple access (TDMA), frequency division multiple access (FDMA), orcode division multiple access (CDMA), or various combinations thereof.

One possible communication protocol that may be used for communicatingacross the O-interface 560 in one embodiment of the present invention isdepicted in FIG. 23. The protocol depicted in FIG. 23 makes use of timedivision multiple access (TDMA) and spread spectrum techniques. As shownin FIG. 23, a polling loop 1380 (“major frame”) comprises a plurality oftime slots 1381 (“minor frames”). Each minor frame 1381 comprisescommunication between a base station (e.g., cellular station) and a userstation (e.g., mobile user) in time division duplex—that is, the basestation transmits to a user station and the user station transmits backto the base station within the same minor frame 1381.

Another communication protocol that may be used for communication acrossthe O-interface 560 is depicted in FIG. 24. The protocol depicted inFIG. 24 uses aspects of both FDMA (in the sense that transmissions aredistinguished by different frequency allocations) and TDMA (in the sensethat transmissions are distinguished by separate time allocations). Asshown in FIG. 24, one frequency band 1510 is allocated to a base station109 for base-to-user transmissions, and another frequency band 1511 isallocated to user stations (e.g., handsets, or other wireless units) foruser-to-base transmissions. A repeating major time frame (or “pollingloop”) 1501 is defined for communication over each frequency band 1510,1511. A plurality (e.g., sixteen) of base time slots 1502 and user timeslots 1503 are defined within the repeating major time frame 1501, withthe user time slots 1503 preferably lagging behind the base time slots1502 by an amount of time. In a preferred embodiment, in which sixteenbase time slots 1502 and sixteen user time slots 1503 are defined ineach major time frame 1501, the time lag 1505 between the first basetime slot 1502 and first user time slot 1503 is a preset amount of timecorresponding to a number of time slots, such as eight time slots, andis therefore referred to as a “slot offset.”

In one aspect of a preferred communication protocol, a single base timeslot 1502 and a single user time slot 1503 collectively comprise aduplex communication channel. In a preferred embodiment, the time frame1501 of the protocol described with reference to FIG. 26 supportssixteen base time slots 1502 and sixteen corresponding user time slots1503, for a total of sixteen possible duplex communication channels. Ina preferred embodiment, each base time slot 1502 and user time slot 1503is 1.35 milliseconds in duration, and each time slot permits 9.6kilobits/second for the transmission of encoded speech or other data.

Details of a preferred I-interface 561 may be found in, e.g., U.S.patent application Ser. No. 08/610,193 filed on Mar. 4, 1996, herebyincorporated by reference as if set forth fully herein; further detailsof the I-interface are also discussed herein with respect to FIG. 5.

The N-interface 562 connects the base station 109 to the base stationcontroller 112, and comprises both traffic and signaling communicationchannels. At the physical layer, the N-interface 562 uses a fractionalT1 service as the transport mechanism. Each fractional T1 link supportstransfer rates from 64 kilobits/second up to 1.536 megabits/second. Eachtime slot on the T1 link supports up to four 16 kilobit/second bearerchannels. To manage signaling and operations or administrative messagingover the N-interface 562, LAPD terminal endpoint identifiers (TEIs) areused for the transfer of signaling and OAM&P information between thebase station controller 112 and a base station 109, as well as controlinformation between a local management terminal (if provided) and thebase station 109. TEIs are preferably assigned to the base commonfunction (see FIG. 7, described below) and the transceivers whichtransmit and receive messages over the N-interface 562. A base commonfunction TEI is permanently assigned to a T1 time slot on theN-interface 562, and is derived from the T1 time slot number.Transceiver TEIs are semi-permanent and are established fromconfiguration parameters. Different functional entities within the basecommon function and the backhaul transceivers are addressed usingservice access point identifiers (SAPIs). In a particular embodiment, asingle backhaul transceiver is supported by the base station 109, andhence in such an embodiment only one transceiver TEI is used.

FIG. 7 shows in more detail the interface signaling structures for theN-interface 562 used in conjunction with a preferred embodiment of theinvention. As shown in FIG. 7, a base station controller (BSC) 702 isconnected to a base station (OBTS) 703 over a plurality of logical links711 through 715, all of which are, from a physical standpoint,multiplexed onto a single digital timeslot channel (or DS0) andtransmitted using pulse code modulation (PCM). The base station 703shown in FIG. 7 comprises two transceivers 706, 707 (designated “TRX1”and TRX2,” respectively), which are identified by terminal endpointidentifiers TEI B and TEI C, respectively, and a base common function(BCF) 705, which is identified by terminal endpoint identifier TEI A.

Signaling messages for traffic control are transmitted on two of thelogical links 713 and 715, one of each connected to transceivers 706 and707. Signaling messages carried by logical links 713 and 715 forinteractions between the base station 703 and base station controller702 relate to functions such as, for example, backhaul and radioresource management, and mobility management. Signaling messages carriedby channels 713 and 715 also relate to end-to-end call control andmobility management signaling between the wireless access communicationunit 106 and the MSC 116, and are encapsulated within transport notes.In addition, observation counters and operation measurements sent by thebase station 703 to the base station controller 702, and encapsulatedwithin transport notes, can be conveyed across logical links 713 and715.

Messaging related to management functions (such as OAM&P) is carried onlogical links 711, 712 and 714, to the base common function 705 andtransceivers 706 and 707, respectively. The OAM&P messaging provides formanagement of the base station 703 by the base station controller 703.

Details of the GSM A-interface are described in, for example, “MobileSwitching Center (MSC) to Base Station Subsystem (BSS) Interface; Layer3 Specification,” GSM Recommendation 08.08. Preferably, somemodifications are made to the standard GSM A-interface to support thefeatures and functionality of the preferred embodiment or embodimentsdescribed herein. Such modifications may include, for example, using aT1 line as the physical interface to carry both traffic and signaling,and using μ-law coding in certain geographical regions (such as NorthAmerica).

Signaling links for the A-interface, in general, logically run betweenthe base station controller 112 and the MSC 116, whereas the bearerlinks span between the transcoding unit 115 and the MSC 116. Thetranscoding unit 115, as noted, processes the 16 kilobits/second bearerlinks received over the T-interface, and generates 64 kilobits/secondpulse-code modulation links towards the MSC 116. The A-interfacesignaling channels carry signaling connection control part (SCCP)logical signaling links. An SCCP link is maintained between the basestation controller 112 and the MSC 116 for each active CPE trunk (or“logical mobile station”) of the wireless access communication unit 106that is communicating with the PSTN 125. Signaling information carriedover the A-interface includes SS7 signaling between the base stationcontroller 112 and the MSC 116 for management of the link, A-interfaceradio resource management signaling, A-interface mobility managementsignaling, call control signaling between the wireless accesscommunication unit 106 and the MSC 116 relayed through the base stationcontroller 112, and, optionally, OAM&P signaling between the basestation controller 112 and the OMC 120. The A-interface signalingtraffic passes through the transcoding unit 115 (if provided), and thetranscoding unit 115, as noted, relays the signaling informationtransparently between the base station controller 112 and the MSC 116.

As noted previously herein, both GSM and non-GSM aspects of signalingare utilized in a preferred communication system 101 in accordance withthe present invention. In a preferred embodiment, aspects of GSMsignaling and messaging are used within the communication system 101such that the interworkings of the physical protocol are essentiallytransparent at the network level. In this embodiment, a non-GSM physicallayer is employed, while communication with the MSC is packaged using aGSM signaling format so that the non-GSM aspects of the wireless systemare transparent to the network. Details of the various interfaces usedin a preferred system have been described above, while details ofsignaling and protocols carried out within the communication system 101are described in more detail below. While the signaling and protocolsare described with reference to the specific interfaces shown in FIGS.1, 7 and 10, aspects of the signaling and protocols may also be employedusing other interface configurations as well.

FIG. 8 is a diagram showing a protocol architecture for one particularembodiment of the preferred communication system 101, and furtherdepicts a preferred relationship of connections among the wirelessaccess communication unit 106, base station 109, base station controller112, and MSC 116 across the O-interface 560, N-interface 562 andA-interface 571. In the protocol architecture shown in FIG. 8, “CM”relates to connection management, “MM” relates to mobility management,“OTA” relates to the over-the-air protocol, “LAPD” relates to linkaccess protocol for the D channel, “IWF” relates to an interworkingfunction, “Ph L” relates to the physical layer, “BSSMAP” relates to thebase station subsystem management application part, “SCCP” relates toSS7 signaling connection control part, “MTP” relates to message transferpart (MTP Layers 2 and 3), “OAM” relates to operations, maintenance andadministration, “NTS-MM” relates to N-Notes mobility management, and“NTS-RR7” relates to N-Notes radio resource management.

The call control protocol is the GSM direction transfer application part(DTAP) call control entity, shown as the GSM-CM layer in FIG. 8. ThisGSM DTAP call control entity (i.e., GSM-CM layer) supports a variety offeatures, including (1) the establishment, maintenance and release ofnormal outgoing voice calls (i.e., originating from the CPE 105) betweenthe wireless access communication unit 106 and the MSC 116; (2) theestablishment, maintenance and release of emergency (i.e., “911”)outgoing voice calls between the wireless access communication unit 106and the MSC 116; and (3) the signaling of DTMF tones from the CPE 105 inthe network direction during active calls. Preferably, transparent digittransmission is provided between the wireless access communication unit106 and the base station 109, since digit analysis is preferably carriedout at the base station 109. Further, the system also preferablyprovides transport capability via control transfer (CT-TRA) O-Notes forDTAP protocol messages.

A GSM DTAP mobility management entity, shown as the GSM-MM layer in FIG.8, is used end-to-end (between the wireless access communication unit106 and the MSC 116) to run various mobility management procedures,including authentication and subscriber identification. Other mobilitymanagement procedures are-supported on the O-interface 560 and theN-interface 562 as part of the protocols utilizing O-Notes and N-Notes,and are shown as the OTA-MM entity and NTS-MM entity in FIG. 8. Theseother mobility management procedures include location updating ornetwork-level registration (both normal and periodic), IMSI detach orde-registration, temporary mobile subscriber identity (TMSI)reallocation, and mobility management connection establishment (for bothnormal and emergency calls). These mobility management proceduresundergo interworking within the base station 109 and the base stationcontroller 112, and the base station controller 112 converts these intothe corresponding GSM mobility management procedures over theA-interface 571. In addition, base-level registration (both normal andperiodic) between the wireless access communication unit 106 and thebase station 109 is supported according to the O-Notes mobilitymanagement procedure.

The GSM-CM and GSM-MM protocol runs end-to-end between the wirelessaccess communication unit 106 and the MSC 116, and the protocol messagesare relayed transparently through the base station 109 and the basestation controller 112. The protocol messages may be encapsulated withintransport O-Notes (CT-TRA) messages across the O-interface 560,transport N-Notes messages across the N-interface 562 using the LAPDsignaling link between the base station 109 and base station controller112, and BSSMAP messages over the A-interface 571 using the SCCPsignaling link.

The over-the-air mobility management procedures are interworked in thebase station 109 with N-Notes mobility management procedures, shown asthe NTS-MM Layer in FIG. 8. The NTS-MM procedures run over the LAPDsignaling link of the N-interface 562, and are interworked in the basestation controller 112 with corresponding DTAP mobility management(GSM-MM) procedures on the A-interface 571. The GSM-MM protocoltherefore runs partly end-to-end between the wireless accesscommunication unit 106 and the MSC 116, and partly between the basestation controller 112 and the MSC 116.

Over-the-air radio resource management functions are provided by an OTAradio resource (OTA-RR) management protocol entity shown in FIG. 8. Suchradio resource management functions include link acquisition, lost linkrecovery, bearer message ciphering, over-the-air slot negotiation andtime slot interchange (in a TDMA system), digit transmission andanalysis, assignment and mode change, link release (whether initiated bythe network or wireless access communication unit 106), base assistinformation, and surrounding base table information. On the O-interface560, the radio resource management

On the N-interface 562, the signaling link is based on the LAPDprotocol. Over the A-interface 571, the BSSMAP messages are carried overSCCP connections. The SCCP and MTP layers are used to provide a robustsignaling link between the base station controller 112 and the MSC 116.

Mobility management connection establishment for normal calls isinitiated by the mobility management entity (i.e., GSM-MM entity shownin FIG. 8) of the wireless access communication unit 106. To do so, themobility management entity sends a Connection Management (CM) ServiceRequest message to the MSC 116, with the Service Type field indicating anormal call. The MSC 116 responds by sending a CM Service Acceptmessage. Upon receiving a CM Service Accept message from the MSC 116,the wireless access communication unit 106 continues with normal callset-up, as further described herein and/or in related patentapplications incorporated by reference elsewhere herein.

For normal calls, the mobility management connection establishmentprocedure may encompass an authentication procedure. Such a proceduremay be based on the DTAP mobility management signaling forauthentication, and may run end-to-end between the MSC 116 and thewireless access communication unit 106.

For emergency (i.e., “911”) calls, the mobility management entity (i.e.,GSM-MM entity shown in FIG. 8) of the wireless access communication unit106 initiates a mobility management connection establishment procedureby sending a CM Service Request message, with the CM Service Type fieldindicating an emergency call, to the MSC 116. In response, the MSC 116transmits a CM Service Accept message to the wireless accesscommunication unit 106. Upon receiving the CM Service Accept messagefrom the MSC 116, the wireless access communication unit 106 continueswith emergency call setup. For emergency calls, the network need notinvoke an authentication procedure.

If the service request is rejected by the MSC 116, or if a servicerequest time-out expires, the wireless access communication unit 106 mayissue a reorder tone to the CPE 105, and abort the call establishmentprocedure.

Although the wireless access communication unit 106 preferably utilizesa mobility management connection establishment procedure in theestablishment of a call connection, the CPE trunks typically do notconstitute mobile components of the system. The communication system 101adapts techniques utilized in a mobile communication system forfacilitating setup and maintenance of a wireless trunk 108 through thewireless access communication unit 106, as generally described herein.Using aspects of a mobile communication system in the communicationsystem 101 which includes the wireless access communication unit 106 hasthe advantage of allowing existing mobile communication systeminfrastructures to support a wireless trunk in accordance with thepresent invention, without requiring a separate base station subsystemor other dedicated wireless path to the PSTN 125 to be constructed.

After the mobility management connection establishment procedure hasbeen completed, the wireless access communication unit 106 exchangesDTAP signaling with the MSC 116 to set up an outgoing call. The primarydifference between normal and emergency call setup procedures is in theway the call is initiated. For a normal call, the wireless accesscommunication unit 106 sends a DTAP Setup message to the base station109 with the Called Address field empty. The base station 109 fills inthe Called Address field of the Setup message with the digits storedearlier as part of the digit analysis procedure, before relaying theSetup message to the MSC 116 across the base station controller 112. Foran emergency call, the wireless access communication unit 106 sends aDTAP Emergency Setup message to the MSC 116. The DTAP Emergency Setupmessage is relayed transparently through the base station 109 and thebase station controller 112. The MSC 116 returns a DTAP Call Proceedingmessage to indicate acceptance of the call request.

If the wireless access communication unit 106 receives a DTAP Progressmessage from the MSC 116 indicating PSTN interworking, the wirelessaccess communication unit 106 connects its speech path between the CPEtrunk and the wireless communication link (e.g., an over-the-air timeslot, if the wireless communication channel is a TDMA time slot). Thewireless access communication unit 106 then expects the call progresstones (busy/ringback) to arrive from the network (i.e., PSTN 125)inband. As the call progresses, the wireless access communication unit106 translates the call progress signals received from the MSC 116 toappropriate tones or signals on the CPE trunk.

If the wireless access communication unit 106 receives a DTAP Alertingmessage from the MSC 116, the wireless access communication unit 106generates a ringback tone towards the CPE 105. The tone is removed undercertain conditions, including: (1) a DTAP Connect message is receivedfrom the MSC 116, indicating that the called user has answered the call;(2) the call is cleared from the network end, with a DTAP Disconnect orRelease Complete message; (3) the call is released via a link level(over-the-air) release; (4) timer expiry occurs at the wireless accesscommunication unit 106; or (5) the wireless access communication unit106 detects an on-hook indication from the CPE 105.

If the wireless access communication unit 106 receives a DTAP Disconnector Release Complete message, indicating that the called party is busy,the action by the wireless access communication unit 106 depends onwhether or not there is PSTN interworking. If the wireless accesscommunication unit 106 has received no indication of PSTN interworking,the wireless access communication unit 106 issues a busy tone to the CPE105 and starts a busy tone timer. The busy tone is removed by thewireless access communication unit 106 if it detects an on-hookindication from the CPE 105, or upon expiration of busy tone timeoutperiod timed by the busy tone timer. If, on the other hand, there isPSTN interworking when an indication is received that the called partyis busy, a busy tone is issued inband over the bearer path by the PSTN125, and is relayed through the wireless access communication unit 106all the way to the CPE 105.

If the wireless access communication unit 106 receives a DTAP Connectmessage from the network, indicating that a connection has beenachieved, the wireless access communication unit 106 connects the bearerpath if it has not already done so, and returns a DTAP ConnectAcknowledgment message to the PSTN 125.

In the event of an exception condition during call establishment, thewireless access communication unit 106 aborts the call establishmentprocedure. For a ground-start CPE trunk, it also passes a disconnectindication to the CPE 105.

While one or more embodiments have been described above in accordancewith various aspects of the present invention, a number of variations ofthese embodiments exist incorporating the same or similar principles ofoperation as described herein. For example, it will be apparent to oneskilled in the art that the functionality of the CPE 105 and thewireless access communication unit 106 can be combined into a singleunit. Also, one or more telephone stations 102 can be connected directlyto the wireless access communication unit 106, bypassing the CPE 105.Also, the CPE 105 need not be connected to the telephone stations 102with telephone lines, but may be wirelessly connected thereto (i.e., awireless PBX).

In addition, the principles of the present invention need not be limitedto use with a wireless access communication unit 106 such asspecifically described herein. Aspects of the invention may be employedfor the purpose of transmitting digits over many types of communicationpaths, particularly those which have a wireless link as part of thecommunication path.

While preferred embodiments of the invention have been described herein,many variations are possible which remain within the concept and scopeof the invention. Such variations would become clear to one of ordinaryskill in the art after inspection of the specification and the drawings.The invention therefore is not to be restricted except within the spiritand scope of any appended claims.

1. A method of communication comprising: generating a repetitive timeframe at a base station; generating a plurality of time slots in therepetitive time frame; assigning one of the plurality of time slots ondemand to a wireless communication unit for communication with the basestation; establishing a call between the wireless communication unit andthe base station; transmitting and receiving call information between anon-wireless unit and the base station using the wireless communicationunit as an intermediary; during the call, receiving dual-tonemulti-frequency (DTMF) tones at the wireless communication unit from thenon-wireless unit; for each of the DTMF tones, formatting a plurality ofdirect transfer application part (DTAP) messages indicating the startand the end of the DTMF tone; for each of the DTMF tones, transmittingthe plurality of DTAP messages from the wireless communication unit tothe base station; conveying the DTAP messages from the base station to aremote location; and translating the DTAP messages back into DTMF tonesignals at the remote location.
 2. The method of claim 1, wherein thenon-wireless unit comprises a local area telephone switch, the methodfurther comprising receiving the DTMF tones at the local area telephoneswitch from a user who is connected to the local area telephone switch.3. The method of claim 1, wherein the non-wireless unit comprises atelephone.
 4. The method of claim 1, wherein the plurality of DTAPmessages comprise at least one DTAP Start-DTMF message and at least oneDTAP Stop-DTMF message.
 5. The method of claim 1, further comprisingsending DTAP acknowledgement messages from the base station to thewireless communication unit in response to acknowledgement of receptionof the DTAP messages at the remote location.
 6. A wireless communicationunit comprising: a subscriber port; a subscriber interface connected tothe subscriber port, the subscriber port comprising a tone detector anda timer; a radio transceiver; and a controller connected to the radio,the controller to cause a wireless connection be established between theradio transceiver and a base station in response to a call request froma non-wireless unit connected to the subscriber interface, wherein: arepetitive time frame is generated at a base station and a plurality oftime slots are generated in the repetitive time frame, with one of theplurality of time slots being assigned to the wireless communicationunit for communication with the base station; call information istransmitted between a non-wireless unit and the base station using thewireless communication unit as an intermediary; dual-tonemulti-frequency (DTMIF) tones are received at the wireless communicationunit from the non-wireless unit; for each of the DTMF tones, thewireless communication unit formats a plurality of direct transferapplication part (DTAP) messages to indicate the start and the end ofthe DTMF tone; the wireless communication unit transmits the pluralityof DTAP messages to the base station and the plurality of DTAP messagesare conveyed from the base station to a remote location; and the DTAPmessages are translated back into DTMF tone signals at the remotelocation.
 7. The wireless communication unit of claim 6, wherein thenon-wireless unit comprises a local area telephone switch, and whereinthe DTMLF tones are received at the local area telephone switch from auser who is connected to the local area telephone switch.
 8. Thewireless communication unit of claim 6, wherein the non-wireless unitcomprises a telephone.
 9. The wireless communication unit of claim 6,wherein the plurality of DTAP messages comprise at least one DTAPStart-DTMIF message and at least one DTAP Stop-DTMF message.
 10. Thewireless communication unit of claim 6, further wherein DTAPacknowledgement messages are sent from the base station to the wirelesscommunication unit in response to acknowledgement of reception of theDTAP messages at the remote location.
 11. A machine-readable mediumhaving stored thereon data representing sequences of instructions that,when executed by a processor, cause the processor to perform operationscomprising: generating a repetitive time frame at a base station;generating a plurality of time slots in the repetitive time frame;assigning one of the plurality of time slots on demand to a wirelesscommunication unit for communication with the base station; establishinga call between the wireless communication unit and the base station;transmitting and receiving call information between a non-wireless unitand the base station using the wireless communication unit as anintermediary; during the call, receiving dual-tone multi-frequency(DIMIF) tones at the wireless communication unit from the non-wirelessunit; for each of the DTMF tones, formatting a plurality of directtransfer application part (DTAP) messages indicating the start and theend of the DTMF tone; for each of the DTMF tones, transmitting theplurality of DTAP messages from the wireless communication unit to thebase station; conveying the DTAP messages from the base station to aremote location; and translating the DTAP messages back into DTMF tonesignals at the remote location.
 12. The medium of claim 11, wherein thenon-wireless unit comprises a local area telephone switch, furthercomprising instructions that, when executed by the processor, cause theprocessor to perform operations comprising receiving the DTMF tones atthe local area telephone switch from a user who is connected to thelocal area telephone switch.
 13. The medium of claim 11, wherein thenon-wireless unit comprises a telephone.
 14. The medium of claim 11,wherein the plurality of DTAP messages comprise at least one DTAPStart-DTMF message and at least one DTAP Stop-DTMF message.
 15. Themedium of claim 11, further comprising sending DTAP acknowledgementmessages from the base station to the wireless communication unit inresponse to acknowledgement of reception of the DTAP messages at theremote location.